The turbine section of a gas turbine engine includes an assembly of alternate rows of static vanes and rows of rotating blades. The rows of blades are mounted to the outer peripheries of respective discs, each disc and its row of blades being known as a stage. The interstage volume between adjacent discs is enclosed by an interstage seal extending between the outer peripheries of the discs.
FIG. 1 shows a schematic longitudinal cross-section through part of the turbine section of a conventional gas turbine engine. The turbine section has a row of intermediate pressure (IP) blades 1 mounted to an IP disc 2, and rows of low pressure (LP) blades 3 mounted to respective LP discs 4. A row of static vanes 5 separates the row of IP blades from the forwardmost row of LP blades, and further rows of static vanes 6 separate the rows of LP blades from each other.
Between the LP discs 4, the interstage volumes are enclosed by seals formed by platforms 7 at the inner sides of the static vanes 6. In addition, interstage seals 8 are bolted or doweled to rails 9 which extend from the bases of the static vanes 6 to perfect labyrinth seals 10 carried by intermediate discs 11.
Between the IP disc 2 and the forwardmost LP disc 4, the interstage volume is enclosed by forward 12 and aft 13 interstage seals which are bolted or doweled to forward and aft rails 14 which extend from the bases of the static vanes 5. These interstage seals extend respectively forward and aft to contribute to air seals at the outer peripheries of the IP disc and the forwardmost LP disc. The platforms 15 at the inner sides of the static vanes 5 also contribute to these air seals.
A problem can arise, however, that the bolts or dowels attaching the interstage seals to the static vane rails can be costly items if they are to be capable of being used at high core temperatures. Alternatively, more complicated interstage seal configurations may be required to protect the bolts or dowels from high core temperatures if the bolts or dowels rated are only capable of being used at low temperature.